import: put a time-out on downloads

Let's abort downloads when they are stuck by setting a download speed
threshold (as suggested in the CURL docs)

Fixes: #14215

src/import/curl-util.c

@@ -247,6 +247,12 @@ int curl_glue_make(CURL **ret, const char *url, void *userdata) {
         if (curl_easy_setopt(c, CURLOPT_FOLLOWLOCATION, 1L) != CURLE_OK)
                 return -EIO;
 
+        if (curl_easy_setopt(c, CURLOPT_LOW_SPEED_TIME, 60L) != CURLE_OK)
+                return -EIO;
+
+        if (curl_easy_setopt(c, CURLOPT_LOW_SPEED_LIMIT, 30L) != CURLE_OK)
+                return -EIO;
+
         *ret = TAKE_PTR(c);
         return 0;
 }